Various types of magnetic field sensing elements are known, including Hall Effect elements and magnetoresistance elements. Magnetic field sensors generally include a magnetic field sensing element and other electronic components. Some magnetic field sensors also include a permanent magnet in a so-called “back biased” arrangement described more fully below.
Magnetic field sensors provide an electrical signal representative of a sensed magnetic field, e.g., a magnitude of the sensed magnetic field. In some embodiments that have the magnet in a back-biased arrangement, a magnetic field sensed by a magnetic field sensor is a magnetic field generated primarily by the magnet. In these back-biased arrangements, in the presence of a ferromagnetic object, the magnetic field generated by the magnet and sensed by the magnetic field sensor varies in accordance with proximity of the ferromagnetic object to the magnetic field sensor.
In some arrangements, the output signal from the magnetic field sensor is a “non-linear” two state signal having a first state indicative of a ferromagnetic object being distal from the magnetic field sensor and a second different state indicative of the ferromagnetic object being proximate to the magnetic field sensor. In other arrangements, the output signal from the magnetic field sensor is a “linear” (analog or digital) signal having a signal value indicative of a distance between the ferromagnetic object and the magnetic field sensor. A magnetic field sensor having either of the above signal characteristics can be referred to as a “proximity sensor.”
Conventional back-biased proximity sensors are able to sense a proximity of a ferromagnetic object (i.e., distance between the back biased proximity sensor and the ferromagnetic object) but are not able to identify a location of the ferromagnetic object, for example, a location in an x-y plane of the back-biased proximity sensor, for example, where the ferromagnetic object approaches the magnetic field sensor in a z direction.
It would be desirable to provide a back-biased proximity sensor that it able to sense not only a proximity of a ferromagnetic object (i.e., distance between the back biased proximity sensor and the ferromagnetic object) but is also able to identify a location of the ferromagnetic object, for example, a location in an x-y plane of the back-biased proximity sensor, for example, where the ferromagnetic object approaches the magnetic field sensor in a z direction.
Conventional back-biased proximity sensors typically use a single ended configuration with one magnetic field sensing element, typically a planar Hall effect element, with a maximum response axis that intersects the ferromagnetic object. In other back-biased arrangements, two or more magnetic field sensing elements are used and a difference signal is generated from the two or magnetic field sensing elements. The difference signal is representative of an edge of a feature (e.g., gear tooth) of the ferromagnetic object.
It would be desirable to provide a back-biased proximity sensor that uses a different type of magnetic field sensing element, different than a planar Hall effect element, and with a maximum response axis that does not intersect the ferromagnetic object.
It is known that differential arrangements can offer advantages not found in conventional back-biased proximity sensors. For example, in general, a differential arrangement that uses two magnetic field sensing elements can be non-responsive to undesirable external magnetic fields that are equally received by the two magnetic field sensing elements. The differential arrangement provides common mode rejection.
A differential arrangement using two planar Hall effect elements would not function properly as a proximity sensor, because both of the two planar Hall effect elements would respond in the same way to a proximate ferromagnetic object and a resulting differential combination would have no output.